The long-term goal of the proposed research is to understand the neurochemistry of spatial attention. In order to do this, we will use in vivo voltammetry to measure micromolar changes in concentration of dopamine and norepinephrine with 50 msec temporal resolution. The method will be used in Rhesus monkeys trained to shift their attention to various environmental stimuli while maintaining visual fixation. Control procedures using catecholamine depleting drugs will be employed to determine the identity of the transmitter that produces the observed voltammetric changes. Previous work in the neurochemistry of attention has largely ignored the dynamic nature of the attention shifting process. The present work overcomes these problems by the use of human chronometric methods (Posner paradigm) that allow assessment of both the attentional and arousal components of attention shifting. The temporal resolution of the high speed voltammetric method is comparable to the speed of the attentional shifts revealed by the Posner paradigm. The involvement of catecholamines in many disorders with attentional components, including Parkinson's disease, attention deficit disorders, and closed head trauma has been clearly established. While our study is not likely to find cures for these disorders, it could provide a rational basis for pharmacological treatments of the attentional components of these disease states.